CHAPTER VI. 



THE SPECIFIC PRECIPITINS. 



The announcement by Widal,' that typhoid bacilli, killed by a 

 heat of 56°, are still agglutinated with the homologous serum, led 

 Kraus * to try the effect of an homologous serum on a filtered bac- 

 terial culture, and this experiment was the beginning of our knowl- 

 edge of the specific precipitins. Cultures of the cholera bacillus 

 were freed from germs by filtration through porcelain, and after 

 having been proved to be sterile were treated with different quanti- 

 ties of a sterile cholera serum. When these two fluids were mixed 

 the mixture became cloudy and after a while filled with fine floccules 

 which gradually subsided, leaving a supernatant clear fluid. Fur- 

 ther investigation showed that the germ-free bacterial culture and 

 the serum must be homologous in order to obtain this precipitation. 

 A serum obtained from an animal which has been rendered immune 

 to the cholera bacillus gives a precipitate when added to filtered cul- 

 tures of the cholera bacillus, but gives no cloudiness when added to 

 like cultures of any other germ. It was also found that the serum 

 of non-immunized animals does not give precipitates with the filtered 

 cultures of any of the pathogenic bacteria. Kraus extended his in- 

 vestigations using the sera and filtered cultures not only of cholera, 

 but also of typhoid fever and the plague, and found that the reaction 

 observed by him was a specific one inasmuch as it was obtained only 

 with homologous sera and bacterial filtrates, and not with heterolo- 

 gous fluids. Furthermore, he demonstrated that the substance in the 

 filtered culture to which this reaction is due exists within the bac- 

 terial cell. This he did by rubbing up cholera bacilli taken from 

 agar cultures with powdered glass and submitting this mixture to a 

 pressure of 300 atmospheres ; the compressed mass was then ex- 

 tracted with alkaline bouillon, diluted and filtered through porcelain, 

 when it was found that this filtrate gave a precipitate with cholera 

 . serum. This shows that the specific reaction observed in these experi- 

 ments for the first time, is due to the presence in the filtrate of a sub- 

 stance extracted from the bacterial cells. Cultures filtered in the ordi- 

 nary way through stone give this reaction because filtrates thus obtained 

 contain substances which originated within the bacterial cells. 

 NiooUe ' repeated, confirmed and extended the observations of 



' La Semaime Med., 1897. 



' Wiener Bin. Wochenschrift, 1897. 



^AnruUes dePInsiUut Pasteur, 12. 



8 113 



